fix for running growpart 2nd time on agent
fix for running growpart 2nd time on agent

Signed-off-by: Nader Ziada <61306b0d4f20cfca7d1222440ff271187de40866@pivotal.io>

uzzz/bosh-agent,gu-bin/bosh-agent,mattcui/bosh-agent,gu-bin/bosh-agent,cloudfoundry/bosh-agent,karafelix/bosh-agent,karafelix/bosh-agent,allomov/bosh-agent,allomov/bosh-agent,mattcui/bosh-agent,mattcui/bosh-agent,gu-bin/bosh-agent,cloudfoundry/bosh-agent,allomov/bosh-agent,uzzz/bosh-agent,uzzz/bosh-agent,karafelix/bosh-agent