Fix /a/common/php symlink creation

Fix the error "updateSymlink: link target
/a/common//usr/local/apache/common-local/php-1.24wmf5 does not exist."
seen during the group1 to 1.24wmf5 deployment by ensuring that the
symlink target is a relative path.

Bug: 64748
Change-Id: I3aafd82da4c7468b555cb311a3cdad77c089dc52
Merge "Fix /a/common/php symlink creation"