[rpmdb] request pk-rpm-db-clean to rebuild db if it exists
[rpmdb] request pk-rpm-db-clean to rebuild db if it exists

/usr/libexec/pk-rpm-db-clean rebuilds rpm db on boot automatically if
/var/lib/PackageKit/scheduled-rebuilddb exists, so ask it to do the
job if it is possible

Signed-off-by: Denis Zalevskiy <43c40921ef02e9bb53daac07eb9ed16452640d88@jolla.com>

sailfishos/sailfish-utilities,raimue/sailfish-utilities,alinelena/sailfish-utilities,sailfishos/sailfish-utilities,Mkaysi/sailfish-utilities,raimue/sailfish-utilities,alinelena/sailfish-utilities,Mkaysi/sailfish-utilities