OpenCV Installation improvements & fixes

[rajat2004]

One of the fixes from the dicussion in #52

[rajat2004]

Travis is passing the opencv builds, but I think it'll be good to do a double check in a Docker container

[rajat2004]

@rsnk96 By any chance, were you able to test these changes in a docker container?
I think both these changes should be good to go, but just confirming

[rsnk96]

Tested once, didn't work out of the box, primarily because run_and_echo() reloads the environment within the bash script effectively, but doesn't update the environment which started the script in the first place (i.e. the shell process). Easy way around this is to just start a new sub-process with the updated SHELLRC file like here just before the script exits (and this has to be done within an if [[ ! -n $CIINSTALL ]]; then....fi so that Travis doesn't fail with this addition)

Also need to check if OpenCV built with the updated version of FFmpeg, will post an update on that in a while

[rajat2004]

@rsnk96 Ohk, thanks for the detailed explanation and testing, otherwise wouldn't have caught the problem. Would have tested it myself but don't have a very good internet connection right now.
I've Pushed a fix as you described

[rajat2004]

Things are definitely wrong right now -

./opencvDirectInstall.sh: line 30: export: `--variable': not a valid identifier
./opencvDirectInstall.sh: line 30: export: `pkg-config)': not a valid identifier

https://travis-ci.org/rsnk96/Ubuntu-Setup-Scripts/jobs/626129056#L1195
Need to look into this and fix it

[rajat2004]

Error's not there now, changed run_and_echo () { $1 ... } to run_and_echo () { eval $1 ... } to force it to run the embedded commands

[rajat2004]

Lapacke change fixes the Atlas not found problem, the OpenBLAS ones generally need code change
Will try to have a go at some of the other errors in #20

[rsnk96]

Updates looks good, and haha didn't know that there was a version of lapack with an e that has more features. Whenever you feel you've hit a wall wrt fixing the issues in #20, feel free to merge this PR

[rajat2004]

@rsnk96 Fixing the other errors will need more time, will try to do that in another PR, this one has enough things in it already
It'll be good to have another test in a docker container soon, but will merge this for now. Also will update the issue with the current errors