Support custom APPSODY_MOUNT separator

[gireeshpunathil]

Is your feature request related to a problem? Please describe.
Please refer to appsody/appsody#31

Describe the solution you'd like
Please refer to appsody/appsody#31

Describe alternatives you've considered
Please refer to appsody/appsody#31

Additional context
appsody/appsody#338 is raised in appsody, a similar change in controller in this repo would compliment it

[gireeshpunathil]

cc @kewegner

[kylegc]

@gireeshpunathil why would the controller need this? The controller does not run docker commands.

[kewegner]

The controller uses the APPSODY_MOUNTS environment variable in the case there are no APPSODY_WATCH_DIRS.

If we change the value of APPSODY_MOUNTS to have something other than ";" as a separator, the logic in the controller would have to change, because it splits on ";". See line 269 of main.go.

[kylegc]

Ok, so to clarify, adopting the docker --mount syntax to allow colons does NOT need controller changes.

However if as a result we change the APPSODY_MOUNTS separator, then yes the controller needs to support this.

[kewegner]

When this issue is done, we would also want to consider the separator for the APPSODY_WATCH_DIRs and the APPSODY_WATCH_IGNOREDIRS (PATHS). Since those are in a list using ';' as the separator.

[kewegner]

We should address #31 at the same time. Also the changes we made for single mount testing might be affected.

[kewegner]

I have started to code this up and will work with @rykal-nate prior to Friday.