install_ydk.sh: Installation of Python YDK packages should not require root access

[ygorelik]

Expected Behavior

When YDK C++ libraries are shared on a platform by multiple users, each individual user should not require to have root/sudo access in order to install YDK core and gNMI Python package in his/her own virtual environment.

Current Behavior

When YDK installation script is used to install Python packages the user must have sudo access in order to install C++ core and gNMI libraries even though they have been already installed.

System Information

YDK 0.8.5 - 0.8.6.3

[ygorelik]

Separated C++ libraries generation steps for Python and Go programming languages to allow multiple users on single platform use individual Python virtual environments with shared YDK C++ libraries.