Features: Improve Spec format strings (#10556)

* Update spec format to simpler syntax, maintain backwards compatibility
* Switch to new spec.format method throughout internals
* update package files for new format strings
* documentation and minor code cleanup. removed nonsensical variant sigils

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

@@ -397,7 +397,7 @@ def write_rpath_specs(self):
            the compiler used to build the executable."""
         if not self.spec_dir:
             tty.warn('Could not install specs for {0}.'.format(
-                     self.spec.format('$_$@')))
+                     self.spec.format('{name}{@version}')))
             return
 
         gcc = self.spec['gcc'].command

var/spack/repos/builtin/packages/of-adios-write/package.py

@@ -67,7 +67,9 @@ def patch(self):
         add_extra_files(self, self.common, self.assets)
         # Emit openfoam version immediately, if we resolved the wrong version
         # it takes a very long time to rebuild!
-        tty.info('Build for ' + self.spec['openfoam'].format('$_$@$%@+$+'))
+        tty.info('Build for ' + self.spec['openfoam'].format(
+            '{name}{@version}{%compiler}{compiler_flags}{variants}'
+        ))
 
     def configure(self, spec, prefix):
         """Generate spack-config.sh file."""

var/spack/repos/builtin/packages/of-precice/package.py

@@ -42,7 +42,9 @@ def patch(self):
         add_extra_files(self, self.common, self.assets)
         # Emit openfoam version immediately, if we resolved the wrong version
         # it takes a very long time to rebuild!
-        tty.info('Build for ' + self.spec['openfoam'].format('$_$@$%@+$+'))
+        tty.info('Build for ' + self.spec['openfoam'].format(
+            '{name}{@version}{%compiler}{compiler_flags}{variants}'
+        ))
 
     def configure(self, spec, prefix):
         """Generate spack-config.sh file."""