Make module autoload warnings configurable (#2763)

Modules generated by the module creation machinery currently print out
a notice that warnts the user that things are being autoloaded.  In
some situations those warnings are problematic.  See #2754 for
discussion.

This is a first cut at optionally disabling the warning messages:

- adds a helper tothe EnvModule base class that encapsulates the
  config file variable;
- adds a method to the base class that provides a default (empty)
  code fragment for generating a warning message;
- passes the warning fragment into the bit that formats the autoload
  string;
- adds specialized autload_warner() methods in the tcl and lmod
  subclasses;; and finally
- touches up the autoload_format strings in the specialized classes.

lib/spack/spack/modules.py

@@ -438,13 +438,20 @@ def header(self):
     def module_specific_content(self, configuration):
         return tuple()
 
+    # Subclasses can return a fragment of module code that prints out
+    # a warning that modules are being autoloaded.
+    def autoload_warner(self):
+        return ''
+
     def autoload(self, spec):
         if not isinstance(spec, str):
             m = type(self)(spec)
             module_file = m.use_name
         else:
             module_file = spec
-        return self.autoload_format.format(module_file=module_file)
+        return self.autoload_format.format(
+            module_file=module_file,
+            warner=self.autoload_warner().format(module_file=module_file))
 
     def prerequisite(self, spec):
         m = type(self)(spec)
@@ -486,6 +493,10 @@ def remove(self):
                 # removedirs throws OSError on first non-empty directory found
                 pass
 
+    def verbose_autoload(self):
+        configuration = _module_config.get(self.name, {})
+        return configuration.get('verbose_autoload', True)
+
 
 class Dotkit(EnvModule):
     name = 'dotkit'
@@ -537,8 +548,13 @@ class TclModule(EnvModule):
     path = canonicalize_path(
         _roots.get(name, join_path(spack.share_path, 'modules')))
 
+    def autoload_warner(self):
+        if self.verbose_autoload():
+            return 'puts stderr "Autoloading {module_file}"\n'
+        return ''
+
     autoload_format = ('if ![ is-loaded {module_file} ] {{\n'
-                       '    puts stderr "Autoloading {module_file}"\n'
+                       '    {warner}'
                        '    module load {module_file}\n'
                        '}}\n\n')
 
@@ -665,8 +681,13 @@ class LmodModule(EnvModule):
         UnsetEnv: 'unsetenv("{name}")\n'
     }
 
+    def autoload_warner(self):
+        if self.verbose_autoload():
+            return 'LmodMessage("Autoloading {module_file}")\n'
+        return ''
+
     autoload_format = ('if not isloaded("{module_file}") then\n'
-                       '    LmodMessage("Autoloading {module_file}")\n'
+                       '    {warner}'
                        '    load("{module_file}")\n'
                        'end\n\n')