Fix {nagios,monitoring}-plugins-ping confusion

We first try to install nagios-plugins-ping and if we fail we just
install monitoring-plugins-ping.

Change-Id: I5e97dd406dc9289fdb086722fe8c24e95baf329b
Closes-Bug: rhbz#1100037
Closes-Bug: rhbz#1096154
Closes-Bug: rhbz#1101665
Closes-Bug: rhbz#1103695