[minor] heartbeat sanity checks before db insertion in scheduler
[minor] heartbeat sanity checks before db insertion in scheduler

This issue was surfaced in https://bugzilla.mozilla.org/show_bug.cgi?id=1136518
The sanity checks are fairly basic, and could be improved a bit further
by looking into the environment and tag strings.

sunnygkp10/mig,zerosign/mig,vladimirdiaconescu/mig,gdestuynder/mig,mvanotti/mig,deathping1994/mig,jvehent/mig,deathping1994/mig,datachand/mig,vladimirdiaconescu/mig,gdestuynder/mig,jboyer2012/mig,djmitche/mig,gdestuynder/mig,pap/mig,ameihm0912/mig,vladimirdiaconescu/mig,rayyang2000/mig,djmitche/mig,jvehent/mig,pap/mig,rezen/mig,zerosign/mig,mozilla/mig,deathping1994/mig,datachand/mig,mvanotti/mig,jboyer2012/mig,rezen/mig,sunnygkp10/mig,rayyang2000/mig,jboyer2012/mig,jvehent/mig,yvesago/mig,rayyang2000/mig,mozilla/mig,zerosign/mig,mvanotti/mig,jboyer2012/mig,therealkbhat/mig,sunnygkp10/mig,gdestuynder/mig,mvanotti/mig,therealkbhat/mig,vladimirdiaconescu/mig,therealkbhat/mig,ameihm0912/mig,rezen/mig,ameihm0912/mig,datachand/mig,deathping1994/mig,yvesago/mig,mozilla/mig,pap/mig,yvesago/mig,therealkbhat/mig,mozilla/mig,mozilla/mig,pap/mig,rayyang2000/mig,yvesago/mig,jvehent/mig,zerosign/mig,rezen/mig,datachand/mig,sunnygkp10/mig