Simplify pip install options

Using the omit template, we can now better control with pip options we
set.

Change-Id: Id675758efbffb7b9a596bab9c0cccb0e1291c82e
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

defaults/main.yaml

@@ -19,6 +19,6 @@ diskimage_builder_git_version: master
 
 diskimage_builder_install_method: git
 
-diskimage_builder_pip_extra_args: ""
 diskimage_builder_pip_name: diskimage-builder
-diskimage_builder_pip_version:
+# diskimage_builder_pip_extra_args:
+# diskimage_builder_pip_version:

tasks/install/git.yaml

@@ -20,5 +20,5 @@
 
 - name: Pip install diskimage-builder from local git repo.
   pip:
-    extra_args: "{{ diskimage_builder_pip_extra_args }}"
     name: "file://{{ diskimage_builder_git_dest }}"
+    extra_args: "{{ diskimage_builder_pip_extra_args|default(omit) }}"

tasks/install/pip.yaml

@@ -14,13 +14,6 @@
 ---
 - name: Install diskimage-builder using pip.
   pip:
-    extra_args: "{{ diskimage_builder_pip_extra_args }}"
+    extra_args: "{{ diskimage_builder_pip_extra_args|default(omit) }}"
     name: "{{ diskimage_builder_pip_name }}"
-  when: diskimage_builder_pip_version is none
-
-- name: Install diskimage-builder using pip.
-  pip:
-    extra_args: "{{ diskimage_builder_pip_extra_args }}"
-    name: "{{ diskimage_builder_pip_name }}"
-    version: "{{ diskimage_builder_pip_version }}"
-  when: diskimage_builder_pip_version is not none
+    version: "{{ diskimage_builder_pip_version|default(omit) }}"