pip-requires PyCrypto should be >= 2.1.0

We need PyCrypto>=2.1.0 for Random which is used in
heat.common.crypt

Change-Id: Ib951deaca17f972aa70a2a65f6e3ade5fb509981
Signed-off-by: Steven Hardy <shardy@redhat.com>

tools/pip-requires

@@ -9,7 +9,7 @@
 # installed using pip, therefore you will need to install the
 # libxml2-dev(el) and libxslt-dev(el) packages.
 
-PyCrypto
+PyCrypto>=2.1.0
 boto>=2.4.0
 eventlet>=0.9.17
 extras