Adding run_once functionality

[hdahme]

Adds the ability to lock a command to the calling process - with the optional limit that the command can only be run once an interval

Usage

To run the echo command once, across a cluster of servers, and to ensure that it's only run once every 60 seconds

consulate run_once -i 60 echo_hello 'echo hello'
>>> hello
consulate run_once -i 60 echo_hello 'echo hello'
>>> Last run happened fewer than 60 second ago. Exiting

This relies on using consulate's existing acquire_lock function as well as setting a lock with a unique name, such that subsequent executions can reference the last time the command was run

[gmr]

What's going on here? it seems you're neutering the unix socket interface intentionally?

[hdahme]

@gmr I'm trying to simplify the command line arguments when connecting with a unix socket. If we're using sockets, the idea is to read the socket location from Consul's stored environment variable, instead of requiring it over the command line.

I could use the environment variable as the default and override if it's passed in as an arg

[gmr]

This looks good other than removing http+unix. Can you let me know what the thought is in that change?

[hdahme]

@gmr I re-instituted http+unix, and updated this pull request to set the default of the api_host to be api_scheme-specific. Let me know what you think!

[gmr]

Looks reasonable, any chance you can rebase off master?

[hdahme]

@gmr closing this in favour of #57