Display meaningful error messages

[jithine]

What happened:

Many cases Screwdriver displays error messages as it is from underlying SCM or backend layers without any context.
Examples

1. No jobs to run messages when Start button is clicked because jobs are disabled from options.
2. Not found message when deleting pipeline
3. Not found message when starting pipeline.

What you expected to happen:

UI should present meaningful and actionable error messages. For above scenarios UI can display

1. Gray out Start button itself if there are no jobs to start, and/or display message that Cannot run builds because jobs are disabled, goto options page to enable them Or No jobs configured to run for Pull requests. Or No jobs configured to run for commit
2. SCM repository not found. Please reach out to Screwdriver admins to delete.
3. SCM Repository not found. Please reach out to Screwdriver admins

How to reproduce it:

[osaf96]

Hi @jithine , I would love to take a look at this. please assign it to me.

[tkyi]

Could be related to #2768

[osaf96]

@tkyi thanks will take a look