version: getBMCVersion: Support value without quotes

Yocto upstream has removed the quotes from the VERSION_ID value
in os-release[1].
Update getBMCVersion() to support unquoted values.

[1]: http://git.yoctoproject.org/cgit/cgit.cgi/poky/commit/?id=4d98363d59cd422b6357148bc0862256ca2076cb

Closes openbmc/phosphor-bmc-code-mgmt#4

Tested: Added unit test cases and verified on a witherspoon with
        and without quotes.

Change-Id: I904a90a611e43722955fb31b1a4b673b1e6e725f
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
2 files changed