rec: Give a more clear error message if the build fails because python was not found

[omoerbeek]

But don't report an error during configure:

When building from a src tarball you don't need python (the tarball includes the generated files), but that changes if settings/table.py was modified or when building from a github checkout.

Short description

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[coveralls]

Pull Request Test Coverage Report for Build 10960690682

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 30 unchanged lines in 10 files lost coverage.
• Overall coverage increased (+0.006%) to 64.702%

---

Files with Coverage Reduction	New Missed Lines	%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
modules/lmdbbackend/lmdbbackend.cc	2	72.54%
pdns/ws-auth.cc	2	80.8%
pdns/misc.cc	2	63.15%
pdns/dnsdistdist/dnsdist.cc	2	68.36%
pdns/iputils.cc	3	55.45%
pdns/packethandler.cc	3	72.56%
pdns/recursordist/pdns_recursor.cc	3	72.7%
pdns/signingpipe.cc	5	83.11%
pdns/recursordist/test-syncres_cc1.cc	6	89.59%

Totals
Change from base Build 10960020735:	0.006%
Covered Lines:	124833
Relevant Lines:	162222

---

💛 - Coveralls

[paddg]

In our case python2 was installed, but python3 was needed if I remember correctly.

[omoerbeek]

In our case python2 was installed, but python3 was needed if I remember correctly.

Ah, I'll extend the test to include that case then

[paddg]

Ah, TIL "Python 4.0 will probably never come" :)

[omoerbeek]

Ah, TIL "Python 4.0 will probably never come" :)

I plan to be retired by then.