replace sgdisk subprocess calls with a helper

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
remove trailing semicolon

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
use the absolute path for executables if found

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
use the new get_command helper in check_call

Signed-off-by: Alfredo Deza <alfredo@deza.pe>
Merge pull request #932 from ceph/wip-6979

replace sgdisk subprocess calls with a helper

Reviewed-by: Sage Weil <sage@inktank.com>