Install from source not working

[chauhang]

Install from source is not working on a brand new ubuntu 18.04 machine.

Steps to reproduce:

1. Install openjdk
2. Install python 3.7
3. Run python ./scripts/install_from_src.py

Traceback (most recent call last):
  File "./scripts/install_from_src.py", line 10, in <module>
    from scripts import tsutils as ts
ImportError: cannot import name 'tsutils' from 'scripts' (/home/ubuntu/anaconda3/lib/python3.7/site-packages/scripts/__init__.py)

[maaquib]

Update instructions too since install from source now requires both Python and Pip

[maaquib]

torchserve_sanity.py run issue on a fresh EC2 CPU instance. Requires updates to requirements file and install from source instructions. Please move dependency install instructions from scripts readme file to the main doc. The dependencies are all over the place right now and need to be consolidated.

> pip install -U -r requirements.txt

> python torchserve_sanity.py
Traceback (most recent call last):
  File "torchserve_sanity.py", line 4, in <module>
    from scripts.test_sanity import test_sanity
  File "/home/ubuntu/serve/scripts/test_sanity.py", line 3, in <module>
    import nvgpu
ModuleNotFoundError: No module named 'nvgpu'

> pip install nvgpu

> python torchserve_sanity.py
Traceback (most recent call last):
  File "torchserve_sanity.py", line 39, in <module>
    from pygit2 import Repository
ModuleNotFoundError: No module named 'pygit2'

> pip3 install -U pip && pip install pygit2

> python torchserve_sanity.py
...
## In directory: /home/ubuntu/serve | Executing command: pylint -rn --rcfile=./ts/tests/pylintrc ts/.
sh: 1: pylint: not found
## Started torchserve pytests
## In directory: /home/ubuntu/serve | Executing command: python -m pytest --cov-report html:result_units --cov=ts ts/tests/unit_tests
/usr/bin/python: No module named pytest
## TorchServe Linting Failed !
...

> pip install -r requirements/developer.txt

> python torchserve_sanity.py  ## Successful