cubicweb-vcsfile #1251789 local_cache should be store relative to instance data directory [resolved]

when a relative path is specified in the config. Else that may cause pb on setup such as the one we have with on instance for the website, and another on another host, with a different id.

done in1.6.1
load left0.000
closed by#038151bd700c store local_cache relative to cache root specified in config, closes #1251789