Pin requests to 2.25.1 for python3.5

* requests 2.26 just dropped py35 and requests 2.26 just got into the
  build stable.  Thus pin it for release.
* Pin cffi 1.14.6 in requirements.txt used in charm build
  for py35 compatability.

Change-Id: I903fd9477118bdb3c7f8827771c8a8578cbb3a2e

requirements.txt

@@ -6,6 +6,7 @@
 # NOTE(lourot): This might look like a duplication of test-requirements.txt but
 # some tox targets use only test-requirements.txt whereas charm-build uses only
 # requirements.txt
+cffi==1.14.6; python_version < '3.6'  # cffi 1.15.0 drops support for py35.
 setuptools<50.0.0  # https://github.com/pypa/setuptools/commit/04e3df22df840c6bb244e9b27bc56750c44b7c85
 
 # Build requirements

src/build.lock

@@ -116,7 +116,7 @@
       "type": "python_module",
       "package": "requests",
       "vcs": null,
-      "version": "2.26.0"
+      "version": "2.25.1"
     },
     {
       "type": "python_module",
@@ -160,7 +160,7 @@
       "type": "python_module",
       "package": "idna",
       "vcs": null,
-      "version": "3.2"
+      "version": "2.10"
     },
     {
       "type": "python_module",
@@ -213,4 +213,4 @@
       "version": "1.26.7"
     }
   ]
-}
+}

src/wheelhouse.txt

@@ -1,5 +1,7 @@
 # Pin hvac for a consistent response type
 hvac==0.10.1
+requests==2.25.1  # for py35 support
+idna<3.0  # for py35 support
 
 git+https://github.com/openstack/charms.openstack.git@stable/21.10#egg=charms.openstack