buildserver: only include latest m2 when provisioning

I think the `android update sdk` tool is installing all of the m2 files
that are present in the temp cache, and it seems to do it in order of
newest to oldest.  Well done, and I thought that tool couldn't get any
worse.  So only include the latest version of android_m2repository*.zip in
the temp cache.
1 job for buildserver-qemu-kvm in 18 minutes and 25 seconds (queued for 1 minute and 23 seconds)
Status Job ID Name Coverage
passed #4200695