Prefer HW adaptation version as QDeviceInfo::Firmware on Sailfish OS

On Sailfish OS, HW adaptation version is stored in /etc/hw-release.
If the value isn't found, QDeviceInfo::version() returns the kernel
version as before.

Change-Id: If742d2af1f719f45a59f4a937e18590060478651
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>
Prefer VERSION_ID from /etc/os-release as QDeviceInfo::Os

On Sailfish OS, where /etc/hw-release exists, QDeviceInfo::version()
used to wrongly return hardware adaptation VERSION_ID from that file as
the first value discovered by QDeviceInfoPrivate::findInRelease().

Thus, we look into /etc/os-release first. If the version isn't found,
the method resorts to the previous behavior.

Change-Id: Ia10c5d7b9cff83ab3006253931ca5a79f2e7c65f
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>
Strip optional quotation marks from version string

Change-Id: I072ef04026486d2591ef5f5143edb89c4299eb85
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>
Allow searching a term in a specific release file

Change-Id: I4a926c140101165a78107ae9d65f974d1b14b868
Reviewed-by: Lorn Potter <lorn.potter@jollamobile.com>