Introduce mappings between CPUs and target names

Currently when running packstack on a CPU other than x86_64
provision_700.py will download the x86_64 cirros images.

This change introduces a set of helper functions to map from host
[kernel] architecture to the names dib and cirros expect.

Change-Id: I5335deb303fbc4c434a8d69c82344a462f0e1540

packstack/installer/core/arch.py

@@ -0,0 +1,42 @@
+# -*- coding: utf-8 -*-
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+# implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Simple routines to map host architectures as expected by various components.
+"""
+
+import os
+
+
+def kernel_arch():
+    """Return the kernel arch."""
+    return os.uname()[4]
+
+
+def dib_arch():
+    """Return the kernel arch or the more appropriate DiB arch."""
+    DIB_MAP = {
+        'x86_64': 'amd64',
+        'aarch64': 'arm64',
+    }
+    return DIB_MAP.get(kernel_arch(), kernel_arch())
+
+
+def cirros_arch():
+    """Return the kernel arch or the more appropriate cirros arch."""
+    CIRROS_MAP = {
+        'ppc64le': 'powerpc',
+        'aarch64': 'arm',
+    }
+    return CIRROS_MAP.get(kernel_arch(), kernel_arch())