googlestorage: don't use host configuration during tests

Change-Id: Id1415f170dbff650d876fc4c01cff04fb8d41415
osutil: add CAMLI_VAR_DIR for CamliVarDir

Change-Id: Idcb0a32ccc49cf24e61bdb81a4fdb1a0f049595c
camlistored: make test use CAMLI_VAR_DIR instead of tweaking HOME/HOMEPATH/APPDATA

For upcoming change to enable strictness in osutil's use of host paths
during tests.

Change-Id: Ied1602d6dc4f5c92e97f760e04b97cc965610b20