feat(kitchen): use debian-10-master-py3 instead of develop

* Expedite this because `debian-10-develop-py3` is no longer working
  after the new upstream release (`2019.2.2`)
* https://travis-ci.org/myii/template-formula/jobs/602164511#L447-L451

```salt
E: Repository 'https://repo.saltstack.com/py3/debian/9/amd64/latest stretch InRelease' changed its 'Suite' value from 'stable' to 'oldstable'
N: This must be accepted explicitly before updates for this repository can be applied. See apt-secure(8) manpage for details.
STDERR: The command '/bin/sh -c apt-get update' returned a non-zero code: 100
---- End output of docker -H unix:///var/run/docker.sock build -f Dockerfile-kitchen20191024-6404-1oweo2f . ----
Ran docker -H unix:///var/run/docker.sock build -f Dockerfile-kitchen20191024-6404-1oweo2f . returned 100] on default-debian-10-develop-py3
```

ssf/defaults.yaml

@@ -22,8 +22,8 @@ ssf_node_anchors:
             #       An alternative method could be to use:
             #       `git describe --abbrev=0 --tags`
             # yamllint disable rule:line-length
-            title: 'ci(travis): run customised `saltcheck` tests on `develop` instances'
-            body: '* Automated using https://github.com/myii/ssf-formula/pull/83'
+            title: 'ci(kitchen): use `debian-10-master-py3` instead of `develop` [skip ci]'
+            body: '* Automated using https://github.com/myii/ssf-formula/pull/84'
             # yamllint enable rule:line-length
           github:
             owner: 'saltstack-formulas'
@@ -87,8 +87,8 @@ ssf_node_anchors:
           # as numbers (for comparisons)
           # [os           , os_ver, salt_ver, py_ver]
 
-          ### `develop-py3`
-          - [debian       ,  10   ,  develop,      3]
+          ### `develop-py3` => `master-py3`
+          - [debian       ,  10   ,   master,      3]
           # - [debian       ,   9   ,  develop,      3]  # unmaintained
           - [ubuntu       ,  18.04,  develop,      3]
           - [centos       ,   7   ,  develop,      3]
@@ -154,7 +154,7 @@ ssf_node_anchors:
         platforms_matrix:
           # Comments in `platforms` apply here, too
           # [os           , os_ver, salt_ver, py_ver,    inspec_suite]
-          - [debian       ,  10   ,  develop,      3,         default]
+          - [debian       ,  10   ,   master,      3,         default]
           - [ubuntu       ,  18.04,   2019.2,      3,         default]
           - [amazonlinux  ,   2   ,   2019.2,      2,         default]
           - [arch-base    , latest,   2019.2,      2,         default]

ssf/files/default/kitchen.yml

@@ -71,8 +71,8 @@ image: netmanagers/salt-{{ salt_ver }}-py{{ py_ver }}:{{ os | replace('/', '-')
           ) %}
 {%-       do prov_cmds.append('- systemctl enable sshd.service') %}
 {%-     endif %}
-{#-     Specific to `develop` #}
-{%-     if salt_ver == 'develop' %}
+{#-     Specific to `develop` (and the introduction of `master`) #}
+{%-     if salt_ver in ['develop', 'master'] %}
 {%-       if os != 'opensuse/leap' %}
 {%-         do prov_cmds.append('- curl -o bootstrap-salt.sh -L https://bootstrap.saltstack.com') %}
 {%-         do prov_cmds.append('- sh bootstrap-salt.sh -XdPbfrq -x python{0} git {1}'.format(py_ver, salt_ver)) %}
@@ -148,8 +148,12 @@ platforms:
 {%-   set salt_ver = platform[2] %}
 {%-   set py_ver   = platform[3] %}
 {#-   Display comment for each section (based on Salt version) #}
+{#-   Temporarily need to merge `develop` and `master` until the transition is complete #}
 {%-   set linebreak = '\n' %}
 {%-   set comment = '`{0}`'.format(salt_ver) %}
+{%-   if salt_ver in ['develop', 'master'] %}
+{%-     set comment = '`develop` => `master`' %}
+{%-   endif %}
 {%-   if loop.index0 == 0 %}
 {%-     set linebreak = first_linebreak %}
 {%-   endif %}