Issue 518: Add suport of configurable extra volume mounts

[CraneShiEMC]

Change log description

• introduces the hostPathVolumeMounts and emptyDirVolumeMounts options as multiple key-value pairs, separated by commas and each consisting of a <name>=<path> tuple.
• parses the hostPathVolumeMounts and emptyDirVolumeMounts values.
• adds the extracted values to the volumes list and containers' volumeMounts list.

Purpose of the change

Implements #518

Pravega operator should allow to specify "extra" volumes to be mounted into pravega pods, including pravega segment store pods and pravega controller pods. Such volumes may be used to share data between the hosts and containers.

What the code does

The code implements the new pravega options: hostPathVolumeMounts and emptyDirVolumeMounts.
To use "extra" volumes in the pravega pods, in the Pravega options, specify:

• hostPathVolumeMounts to add hostPath volumes
• emptyDirVolumeMounts to add emptyDir volumes

The options consist of multiple key-value pairs, separated by commas and each consisting of a <name>=<path> tuple:

<name> is a volume name, the file or directory.
<path> is where the volume is mounted in the container.
For example, emptyDirVolumeMounts: "heap-dump=/tmp/dumpfile/heap,log=/opt/pravega/logs"

How to verify it

1. Add the emptyDirVolumeMounts option to Pravega options parameter, e.g., emptyDirVolumeMounts: "heap-dump=/tmp/dumpfile/heap,log=/opt/pravega/logs".
2. When the pravega cluster is deployed and ready, make sure that the the volumes list and containers' volumeMounts list has contained the emptyDir volumes and mounts specified in the emptyDirVolumeMounts.

The function has worked as expected on the deployed pravega cluster in our environment.

[codecov-io]

Codecov Report

Merging #517 (6616cc7) into master (c608b78) will decrease coverage by 1.24%.
The diff coverage is 37.03%.

@@            Coverage Diff             @@
##           master     #517      +/-   ##
==========================================
- Coverage   71.75%   70.51%   -1.25%     
==========================================
  Files          15       15              
  Lines        3477     3564      +87     
==========================================
+ Hits         2495     2513      +18     
- Misses        874      931      +57     
- Partials      108      120      +12     

Impacted Files	Coverage Δ
pkg/controller/pravega/pravega_segmentstore.go	91.62% <35.84%> (-8.38%)	⬇️
pkg/controller/pravega/pravega_controller.go	86.29% <38.18%> (-13.71%)	⬇️
pkg/controller/pravegacluster/upgrade.go	71.09% <0.00%> (-0.19%)	⬇️
pkg/apis/pravega/v1beta1/pravega.go	97.80% <0.00%> (+0.07%)	⬆️

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[anishakj]

LGTM