Catch configuring KDE4 variant of umbrello with installed KF5 kdevplatform development package

The KDE4 and KF5 variants of kdevplatform package uses different
versions 1.x (KDE4) and 5.x (KF5), but share the same cmake package
name 'KDevPlatform'. Trying to compile the KDE4 variant with an
installed KF5 kdevplatform package fetches Qt5 and KF5 packages into
cmake build system and results into compile errors.

Specifing "1.7.3" EXACT in the find_package call does not fix the
issue.