[ccache] Shared ccache directory between docker containers

[Anders Björklund]

Ragnar Rova wrote:
> Thanks, i'll try it out. How stable is the memcached support?
>
>>     It would also be interesting to test sharing a cache between containers
>>     on different hosts, by using the "memcached" feature over the network:
>>
>>     https://lists.samba.org/archive/ccache/2016q1/001394.html

It is ready for public testing, all known issues addressed:
https://github.com/jrosdahl/ccache/pull/58

An earlier version of it has been in production for years:
https://github.com/jrosdahl/ccache/pull/30


By default it will still use the file cache, just like before.
You have the option to only use memcached for storing objects.

We are looking for some more testers and for other feedback...
And there's a few minor tweaks being done, but nothing major.

/Anders