Delete build.ninja if ninja-generator fails.
Delete build.ninja if ninja-generator fails.

If creating build.ninja fails, delete the partially built build.ninja
file.

Resolves: LE-12763
Change-Id: I89c71a2929f55f3ec443011303bce03eaaf377f6

legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af,legatoproject/legato-af