Launch browsers by path: --browser /path/to/browser

[flotwig]

Closes #1026

Depends on merging #3225

Todo:

• write tests for the feature
• clean up errors in open mode
• figure out why displayName isn't changing

[flotwig]

cypress open -P ../example-kitchensink --browser /usr/local/bin/chromium:

[flotwig]

@brian-mann Updated the error messages like we talked about. @lilaconlee's changes make details into a cool expando which is much more understandable for the user:

CLI error looks better now too:

[brian-mann]

Love the error, it does look much better. Look what you did @lilaconlee :P

[brian-mann]

Here's a slightly more condensed version of this taking advantage of bluebird...

launcher.detect()
.then (browsers) =>
  _.find(browsers, { family: 'chrome' })
.tap (browser) =>
  if !browser
    throw new Error("A 'chrome' family browser must be installed for this test. None were found.")
.get('path')
## turn binary browser names ("google-chrome") into their absolute paths
## so that server recognizes them as a path, not as a browser name
.then(absPath)
.then (foundPath) =>
  e2e.exec(@, {
    project: Fixtures.projectPath("e2e")
    spec: "simple_spec.coffee"
    browser: foundPath
    snapshot: true
    expectedExitCode: 0
  })

[brian-mann]

I'm going to approve this PR - but this feels like this is something that should be part of the found browsers objects in launcher.

It looks like we have a path property... but apparently that only returns the binary executable and not the actual path to it?