'with_or_without' accepts bool variants

Fixes #4112

This commit extends the support of the AutotoolsPackage methods
`with_or_without` and `enable_or_disable` to bool-valued variants. It
also defines for those functions a convenience short-cut if the
activation parameter is the prefix of a spec (like in
`--with-{pkg}={prefix}`).

This commit also includes:

* Updates to viennarna and adios accordingly: they have been modified to
  use `enable_or_disable` and `with_or_without`
* Improved docstrings in `autotools.py`. Raise `KeyError` if name is
  not a variant.

var/spack/repos/builtin/packages/viennarna/package.py

@@ -27,8 +27,9 @@
 
 class Viennarna(AutotoolsPackage):
     """The ViennaRNA Package consists of a C code library and several
-       stand-alone programs for the prediction and comparison of RNA secondary
-       structures."""
+    stand-alone programs for the prediction and comparison of RNA secondary
+    structures.
+    """
 
     homepage = "https://www.tbi.univie.ac.at/RNA/"
     url      = "https://www.tbi.univie.ac.at/RNA/download/sourcecode/2_3_x/ViennaRNA-2.3.5.tar.gz"
@@ -49,19 +50,12 @@ def url_for_version(self, version):
         return url.format(version.up_to(2).underscored, version)
 
     def configure_args(self):
-        args = []
-        if '+sse' in self.spec:
-            args.append('--enable-sse')
-        else:
-            args.append('--disable-sse')
-        if '~python' in self.spec:
-            args.append('--without-python')
-        else:
-            args.append('--with-python')
-        if '~perl' in self.spec:
-            args.append('--without-perl')
-        else:
-            args.append('--with-perl')
+
+        args = self.enable_or_disable('sse')
+        args += self.with_or_without('python')
+        args += self.with_or_without('perl')
+
         if 'python@3:' in self.spec:
             args.append('--with-python3')
+
         return args