[deviceinfo] allow searching a term in a specific release file
[deviceinfo] prefer VERSION from /etc/os-release as QDeviceInfo::Os

QDeviceInfo::version() used to return VERSION_ID from /etc/hw-release as
a version of the OS, which wasn't quite correct.

If not found, the method resorts to the old implementation.
[deviceinfo] prefer HW adaptation version as QDeviceInfo::Firmware

If not found in /etc/hw-release, QDeviceInfo::version() returns
the kernel version.
[deviceinfo] strip optional quotation marks from version string