Check that tutorials are executing on build

[svekars]

We want to know if a tutorial is executing while we are building it. For each tutorial, sphinx-gallery prints Total running time (Example at the bottom of the page). The total running time of 0.00 might mean that the tutorial is failing. If this is the case, we want to be able to catch this while we run build.sh and put that output to a text file for further investigation.

@malfet @b0noI @atalman

[malfet]

Probably related #2001 <- updating to newer sphinx-gallery exposes runtime errors

[clee2000]

closing, as #2031 is merged

opened an issue #2033 for reducing the length of the NOT_RUN list