valgrind: suppress eglibc leak of TLS

<error>
  <unique>0xf9</unique>
  <tid>1</tid>
  <kind>Leak_PossiblyLost</kind>
  <xwhat>
    <text>320 bytes in 1 blocks are possibly lost in loss record 248 of 289</text>
    <leakedbytes>320</leakedbytes>
    <leakedblocks>1</leakedblocks>
  </xwhat>
  <stack>
    <frame>
      <ip>0x4C29DB4</ip>
      <obj>/usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so</obj>
      <fn>calloc</fn>
    </frame>
    <frame>
      <ip>0x4012074</ip>
      <obj>/lib/x86_64-linux-gnu/ld-2.15.so</obj>
      <fn>_dl_allocate_tls</fn>
      <dir>/build/buildd/eglibc-2.15/elf</dir>
      <file>dl-tls.c</file>
      <line>297</line>
    </frame>
    <frame>
      <ip>0x5289ABC</ip>
      <obj>/lib/x86_64-linux-gnu/libpthread-2.15.so</obj>
      <fn>pthread_create@@GLIBC_2.2.5</fn>
      <dir>/build/buildd/eglibc-2.15/nptl</dir>
      <file>allocatestack.c</file>
      <line>571</line>
    </frame>
    <frame>
      <ip>0xA6A89A</ip>
      <obj>/usr/bin/ceph-osd</obj>
      <fn>Thread::try_create(unsigned long)</fn>
      <dir>/srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-0.83-444-ge74ad5f/src/common</dir>
      <file>Thread.cc</file>
      <line>112</line>
    </frame>
    <frame>
      <ip>0xA6A94E</ip>
      <obj>/usr/bin/ceph-osd</obj>
      <fn>Thread::create(unsigned long)</fn>
      <dir>/srv/autobuild-ceph/gitbuilder.git/build/out~/ceph-0.83-444-ge74ad5f/src/common</dir>
      <file>Thread.cc</file>
      <line>122</line>
    </frame>

...

ubuntu@teuthology:/a/teuthology-2014-08-13_23:04:01-fs-next-testing-basic-multi/423897

Signed-off-by: Sage Weil <sage@redhat.com>
Merge pull request #312 from ceph/wip-tls-leak

valgrind: ignore TLS leak in glibc