Improve inventory script error messages. (#17589)

When an inventory file looks executable (with a #!) but
isn't, the error message could be confusing. Especially
if the inventory file was named something like 'inventory'
or 'hosts'. Add some context and quote the filename.

This is based on https://github.com/ansible/ansible/pull/15758

lib/ansible/inventory/dir.py

@@ -52,7 +52,6 @@ def get_file_parser(hostsfile, groups, loader):
     except:
         pass
 
-
     #FIXME: make this 'plugin loop'
     # script
     if loader.is_executable(hostsfile):
@@ -62,7 +61,8 @@ def get_file_parser(hostsfile, groups, loader):
         except Exception as e:
             myerr.append(str(e))
     elif shebang_present:
-        myerr.append("The file %s looks like it should be an executable inventory script, but is not marked executable. Perhaps you want to correct this with `chmod +x %s`?" % (hostsfile, hostsfile))
+
+        myerr.append("The inventory file \'%s\' looks like it should be an executable inventory script, but is not marked executable. Perhaps you want to correct this with `chmod +x %s`?" % (hostsfile, hostsfile))
 
     # YAML/JSON
     if not processed and not shebang_present and os.path.splitext(hostsfile)[-1] in C.YAML_FILENAME_EXTENSIONS:
@@ -81,7 +81,7 @@ def get_file_parser(hostsfile, groups, loader):
             myerr.append(str(e))
 
     if not processed and myerr:
-        raise AnsibleError( '\n'.join(myerr) )
+        raise AnsibleError('\n'.join(myerr))
 
     return parser
 
@@ -191,7 +191,6 @@ class InventoryDirectory(object):
                     # info
                     allgroup.child_groups.remove(group)
 
-
     def _add_group(self, group):
         """ Merge an existing group or add a new one;
             Track parent and child groups, and hosts of the new one """
@@ -225,7 +224,7 @@ class InventoryDirectory(object):
 
         # name
         if group.name != newgroup.name:
-            raise AnsibleError("Cannot merge group %s with %s" % (group.name, newgroup.name))
+            raise AnsibleError("Cannot merge inventory group %s with %s" % (group.name, newgroup.name))
 
         # depth
         group.depth = max([group.depth, newgroup.depth])
@@ -246,7 +245,6 @@ class InventoryDirectory(object):
                     if hostgroup.name == group.name and hostgroup != self.groups[group.name]:
                         self.hosts[host.name].groups.remove(hostgroup)
 
-
         # group child membership relation
         for newchild in newgroup.child_groups:
             # dict with existing child groups:
@@ -298,4 +296,3 @@ class InventoryDirectory(object):
         for i in self.parsers:
             vars.update(i.get_host_variables(host))
         return vars
-