ureport: use additional HTTP headers with 'rhsm-entitlement' cert auth

Related to rhbz#1140224

Signed-off-by: Jakub Filak <jfilak@redhat.com>
lib: add strremovech(str, ch)

Related to rhbz#1140224

Signed-off-by: Jakub Filak <jfilak@redhat.com>
testsuite: add test for strremovech(str, ch)

Related to rhbz#1140224

Signed-off-by: Jakub Filak <jfilak@redhat.com>