MFC r315199,r315200,r315203:

r315199:

sbin/dhclient: fix a memory leak in parse_client_lease_statement(..)

The memory stored by lease would have previously been leaked if an
unterminated lease declaration was found in an early-return code path.

CID: 1007114

r315200:

Fix -Wunused-but-set-warning with ret

While here, resolve Coverity warnings by demonstrating that vfprintf's
return value is being explicitly ignored.

Tested with: clang, gcc 4.2.1, gcc 6.3.0

r315203:

sbin/dhclient: fix vendor storage leak in parse_option_decl(..)

This ensures the storage isn't leaked when non-NULL and the function
returns early, prior to the free(vendor) later on in the function.

CID: 1007111-1007113