Merge remote-tracking branch 'remotes/ehabkost/tags/python-next-pull-request' into staging

Require Python >= 3.5 to build QEMU

Python 2 EOL is 11 days away, we will stop supporting
it in QEMU 5.0.

# gpg: Signature made Fri 20 Dec 2019 16:49:02 GMT
# gpg:                using RSA key 5A322FD5ABC4D3DBACCFD1AA2807936F984DC5A6
# gpg:                issuer "ehabkost@redhat.com"
# gpg: Good signature from "Eduardo Habkost <ehabkost@redhat.com>" [full]
# Primary key fingerprint: 5A32 2FD5 ABC4 D3DB ACCF  D1AA 2807 936F 984D C5A6

* remotes/ehabkost/tags/python-next-pull-request:
  configure: Require Python >= 3.5
  travis: Replace Python 3.4 build with 3.5

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>