add ability to use the role on CentOS 7

README.md

@@ -18,6 +18,11 @@ The name of the packge to install to get `pip` on the system. You can set to `py
 
     pip_install_packages: []
 
+The role will try to autodetect pip executable: it will use `pip` for Python 2 and `pip3` for Python 3. You can also override this explicitly:
+
+    pip_executable: pip3.6
+
+
 A list of packages to install with pip. Examples below:
 
     pip_install_packages:

defaults/main.yml

@@ -1,5 +1,5 @@
 ---
 # For Python 3, use python3-pip.
 pip_package: python-pip
-
+pip_executable: "{{ 'pip3' if pip_package.startswith('python3') else 'pip' }}"
 pip_install_packages: []

tasks/main.yml

@@ -10,5 +10,5 @@
     version: "{{ item.version | default(omit) }}"
     virtualenv: "{{ item.virtualenv | default(omit) }}"
     state: "{{ item.state | default(omit) }}"
-    executable: "{{ 'pip3' if pip_package == 'python3-pip' else 'pip' }}"
+    executable: "{{ pip_executable }}"
   with_items: "{{ pip_install_packages }}"