Add basic tests for echo(1)

Verify that echo(1) does not...

• ... print the trailing newline character with option '-n'.
• ... print the trailing newline character when '\c' is appended to the end of the string.

Submitted by: shivansh
Reviewed by: asomers, ngie
MFC after: 1 month
Sponsored by: Google, Inc (GSoC 2017)
Differential Revision: D11036