Moderate: cyrus-sasl security update

[- 2.1.15-15]

• Changed spec file to include the mech patch all the time.
• Added patch to prevent printing null realm
• Applied existing mech for 1.5 to 2.1
  Related: rhbz#189814

[2.1.15-14]

• temporarily back out the fixes for #157012, #190113

[2.1.15-13]

• add unapplied patches which make the DIGEST-MD5 plugins omit the realm
  argument when the environment has
  set to a
  non-zero value, for testing purposes
• add missing build dependency on zlib-devel (#190113)

[2.1.15-12]

• make v1 of the sasl library use /dev/urandom instead of /dev/random, as
  we do in v2 of the library at compile-time (#157012)

[2.1.15-11]

• backport fix for segfault in the digest-md5 module in cases when the
  client didn’t supply a realm (#189814, CVE-2006-1721)