ldap: Fix pipe error

Currently, piping the output of ldaplist to something that doesn't
read till EOF produces a croaking IOError:

| scfc@tools-login:~$ /usr/local/bin/ldaplist passwd | head -2

| dn: uid=80686,ou=people,dc=wikimedia,dc=org
| Traceback (most recent call last):
|   File "/usr/local/bin/ldaplist", line 258, in <module>
|     main()
|   File "/usr/local/bin/ldaplist", line 199, in main
|     print "dn: " + PosixData[i][0]
| IOError: [Errno 32] Broken pipe
| scfc@tools-login:~$

This change makes ldaplist ignore SIGPIPEs.

Change-Id: Ie0679ffd45b178c34c09b75e5e053facae6d867f
Merge "ldap: Fix pipe error" into production