Curl install script improvements

[derekbekoe]

• Change default install location to a user location (e.g. ~/az) instead of global location (usr/local/az)

• Prompt user if they want the script to modify their profile/rc file to update $PATH.

• Fail install with appropriate message if custom install path contains space. Provide user friendly error message to address Installer resolves links and does not handle spaces in paths #1070

• Allow custom profile/rc file to be provided. By defaulting to a user location rather than global, we address Installing on OSX tries to modify root's bash completion, not the user's #1009 as sudo will no longer be required. This work item extends this further so a user provided file can be used.

• Save tab completion script to install location and provide instructions on how user can enable tab completion later (addresses [Install] Download tab completion script even when user turns down tab completion #939).

• After install, check $PATH for az and warn user if another az exists already on the system (e.g. from a pip install or apt-get install). We can warn the user and list the other azs found.

• If installation already exists in target directory, prompt user so we delete the old install directory.

• Curl script should also show a warning/error message if the required native dependencies are not installed.

• Verify Python version (>= 2.7) before proceeding with curl install

Once the above changes have been made:

• Publish updated scripts to storage account so they're publicly available.

[derekbekoe]

#1400 should be part of this change also.

[derekbekoe]

Curl script should also show a warning/error message if the required native dependencies are not installed.
e.g.

Ubuntu 14.04

$ curl -L https://aka.ms/InstallAzureCli | bash
Native dependencies are required that are not currently installed. Please install them with the command below then try again.
“sudo apt-get install -y libssl-dev libffi-dev python-dev”

CentOS

$ curl -L https://aka.ms/InstallAzureCli | bash
Native dependencies are required that are not currently installed. Please install them with the command below then try again.
“sudo yum install -y gcc libffi-devel python-devel openssl-devel”

SUSE OpenSUSE

$ curl -L https://aka.ms/InstallAzureCli | bash
Native dependencies are required that are not currently installed. Please install them with the command below then try again.
“sudo zypper --non-interactive install gcc libffi-devel python-devel openssl-devel”

It can also provide a prompt and then attempt to install the native dependencies.

cc: @johanste, @yugangw-msft, @brendandburns