net-snmp: add ptest package

Issue: TA79430

- Change to use append for PACKAGES so that:
  * ptest package is added from ptest bbcalss
  * the PN is back, allow empty and add rdepends on net-snmp-client
    in case the user try to add net-snmp to the image
- Add a patch to fix the output format for ptest
- Add run-ptest
- Add rdepends on perl for ptest

(LOCAL REV: NOT UPSTREAM) -- Sent to meta-networking on 20150114

Signed-off-by: Jackie Huang <jackie.huang@windriver.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>