Make some memcached arguments (for fluxd) configurable

[hiddeco]

279 took care of the weave-flux-agent arguments, there is however also an edge case scenario in which the default settings for the weave-flux-memcached deployment are insufficient.

E.g. when a Weave Cloud user has thousands of tags for one image, the -I 5m argument must likely be increased as the metadata for all image tags will not fit into this default (and Flux will start logging SERVER_ERROR object too large for cache errors).

The configurability of the following arguments on the memcached deployment would be useful:

• -m (integer)
• -I (string)

A full description of both arguments can be found on the memcached man page.

[bobbytables]

We just hit the error where the object is too big to store in memcache. If you're using GCR like we are, I found a neat script that will delete images older than a certain date:

https://gist.github.com/ahmetb/7ce6d741bd5baa194a3fac6b1fec8bb7