actually check we can run scm command for roles (#43315)

* actually check we can run scm command for roles
* a better error message than file not found
* more narrow exception hanlding
* refactor common functions for more extended use and further 'basic.py' separation

lib/ansible/module_utils/basic.py

@@ -160,6 +160,8 @@ from ansible.module_utils.common._collections_compat import (
     Sequence, MutableSequence,
     Set, MutableSet,
 )
+from ansible.module_utils.common.process import get_bin_path
+from ansible.module_utils.common.file import is_executable
 from ansible.module_utils.pycompat24 import get_exception, literal_eval
 from ansible.module_utils.six import (
     PY2,
@@ -670,20 +672,6 @@ def human_to_bytes(number, default_unit=None, isbits=False):
     return int(round(num * limit))
 
 
-def is_executable(path):
-    '''is the given path executable?
-
-    Limitations:
-    * Does not account for FSACLs.
-    * Most times we really want to know "Can the current user execute this
-      file"  This function does not tell us that, only if an execute bit is set.
-    '''
-    # These are all bitfields so first bitwise-or all the permissions we're
-    # looking for, then bitwise-and with the file's mode to determine if any
-    # execute bits are set.
-    return ((stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH) & os.stat(path)[stat.ST_MODE])
-
-
 def _load_params():
     ''' read the modules parameters and store them globally.
 
@@ -2287,28 +2275,13 @@ class AnsibleModule(object):
            - opt_dirs:  optional list of directories to search in addition to PATH
         if found return full path; otherwise return None
         '''
-        opt_dirs = [] if opt_dirs is None else opt_dirs
 
-        sbin_paths = ['/sbin', '/usr/sbin', '/usr/local/sbin']
-        paths = []
-        for d in opt_dirs:
-            if d is not None and os.path.exists(d):
-                paths.append(d)
-        paths += os.environ.get('PATH', '').split(os.pathsep)
         bin_path = None
-        # mangle PATH to include /sbin dirs
-        for p in sbin_paths:
-            if p not in paths and os.path.exists(p):
-                paths.append(p)
-        for d in paths:
-            if not d:
-                continue
-            path = os.path.join(d, arg)
-            if os.path.exists(path) and not os.path.isdir(path) and is_executable(path):
-                bin_path = path
-                break
-        if required and bin_path is None:
-            self.fail_json(msg='Failed to find required executable %s in paths: %s' % (arg, os.pathsep.join(paths)))
+        try:
+            bin_path = get_bin_path(arg, required, opt_dirs)
+        except ValueError as e:
+            self.fail_json(msg=to_text(e))
+
         return bin_path
 
     def boolean(self, arg):