Auto merge of #2063 - jtgeibel:fastboot/fix-nginx-erb, r=jtgeibel
Auto merge of #2063 - jtgeibel:fastboot/fix-nginx-erb, r=jtgeibel

Fix fastboot check in nginx erb template

In production we're currently returning a 502 Bad Gateway for
`/policies`.  I intend to merge this and deploy to production shortly.

This bug was introduced in #1907.  The bad check always evaluated to
true.  An explicit check for an empty string is added as well.  I've
tested this locally with `erb` and different values and the generated
configuration is now working correctly.

r? @jtgeibel

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