Move Cryptohome mount error code to system_api BUG=chromium-os:16552 TEST=gmerge libcros Change-Id: I14f756b802d37ba7c2cbccb2be3ad5ac9c2e5539 Reviewed-on: https://gerrit.chromium.org/gerrit/15481 Reviewed-by: Satoru Takabayashi <[email protected]> Commit-Ready: Ryo Hashimoto <[email protected]> Tested-by: Ryo Hashimoto <[email protected]>