add check for ofed

[jose-d]

https://github.com/jose-d/telegraf-collectors/blob/854968b06ead45a6ef76b33ab66f2cbacb870556/ibmon/give_stats.py#L13

Mar 19 16:56:20 n27 sudo[76850]: pam_unix(sudo:auth): conversation failed
Mar 19 16:56:20 n27 sudo[76850]: pam_unix(sudo:auth): auth could not identify password for [telegraf]
Mar 19 16:56:21 n27 telegraf[3413]: 2020-03-19T15:56:21Z E! [inputs.exec] Error in plugin: exec: exit status 1 for command '/usr/local/sw/monitors/ibmon/give_stats.py':
Mar 19 16:56:30 n27 sudo[76896]: pam_unix(sudo:auth): conversation failed

we should protect us from the situation when there is no ofed installed