Change default smart connection to ssh on macOS and remove paramiko from requirements.txt (#54738)

* Remove default use of paramiko connection plugin on macOS
    This fix was originally to work around a bug that caused a kernel panic on macOS
    that has since been fixed.
* Remove paramiko from requirements.txt
* Move paramiko checking to common place
* Drop the warnings obfiscation code
* Update pip installation instructions to reflect upstream instructions
* Fix tests on CentOS 6 (Python 2.6) that now show Python deprecation warnings
* Add changelog fragment

lib/ansible/modules/network/iosxr/iosxr_user.py

@@ -206,6 +206,7 @@ from copy import deepcopy
 import collections
 
 from ansible.module_utils.basic import AnsibleModule
+from ansible.module_utils.compat.paramiko import paramiko
 from ansible.module_utils.network.common.utils import remove_default_spec
 from ansible.module_utils.network.iosxr.iosxr import get_config, load_config, is_netconf, is_cliconf
 from ansible.module_utils.network.iosxr.iosxr import iosxr_argument_spec, build_xml, etree_findall
@@ -216,15 +217,6 @@ try:
 except ImportError:
     HAS_B64 = False
 
-HAS_PARAMIKO = True
-try:
-    import paramiko
-except ImportError:
-    try:
-        import ansible_paramiko as paramiko
-    except ImportError:
-        HAS_PARAMIKO = False
-
 
 class PublicKeyManager(object):
     def __init__(self, module, result):
@@ -693,7 +685,7 @@ def main():
                 msg='library base64 is required but does not appear to be '
                     'installed. It can be installed using `pip install base64`'
             )
-        if not HAS_PARAMIKO:
+        if paramiko is None:
             module.fail_json(
                 msg='library paramiko is required but does not appear to be '
                     'installed. It can be installed using `pip install paramiko`'