utils.WriteFile: Remove optional check_abspath parameter
utils.WriteFile: Remove optional check_abspath parameter

cfgupgrade will not work with relative paths at all, but rather get them
from constants.py.

Reviewed-by: iustinp


yiannist/ganeti,mbakke/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,yiannist/ganeti,yiannist/ganeti,ganeti/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,mbakke/ganeti,bitemyapp/ganeti,leshchevds/ganeti,ganeti/ganeti,leshchevds/ganeti,andir/ganeti,grnet/snf-ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,bitemyapp/ganeti,onponomarev/ganeti,apyrgio/ganeti,andir/ganeti,dimara/ganeti,onponomarev/ganeti,andir/ganeti,apyrgio/snf-ganeti,apyrgio/ganeti,dimara/ganeti