[mb2] Do not fail if qtc_ macros are missing from spec

Downgraded failure to just a notification. The user can have a
perfectly fine spec file that works without the qtc_ macros,
so it does not make sense to fail the build in that case.

Signed-off-by: Juha Kallioinen <juha.kallioinen@jolla.com>
Merge pull request #5 from sailfish-sdk/qtc-warn

[mb2] Do not fail if qtc_ macros are missing from spec