Update das-client to version 2.5.0 which also add cache option.

See also cms-sw/cmssw#2420.
Merge pull request #411 from degano/das_250

Update das-client to version 2.5.0.
Merge remote branch 'origin/IB/CMSSW_7_1_X/stable' into IB/CMSSW_7_0_X/stable