Fix parsing of drbdsetup show output

This fixes the parsing of integers in the drbdsetup show output with
newer pyparsing versions.

Basically, the convert-to-int action that we use was taken from the
example documentation of an older pyparsing version that automatically
uses only the second element if the result is returned as a tuple, but
this was deprecated for a while and removed in 1.4.3.

Based on a nice report by Jorge Cabello <jorge@aspl.es>, and
confirmation about pyparsing behaviour from its author. Thanks!

Reviewed-by: imsnah