Make access to .vmc_target / .vmc_token / .vmc_instances concurrency safe (STAC uses multiple process that can read / modify these files simultaneously)
Make access to .vmc_target / .vmc_token / .vmc_instances concurrency safe
(STAC uses multiple process that can read / modify these files simultaneously)

Change-Id: I0c2fa38104e7018a97f6891b18aff3b08eaf5a5d

ack/af