scylla-gdb.py: restore python2 compatibility
scylla-gdb.py: restore python2 compatibility

Although python2 should be a distant memory by now, the reality is that
we still need to debug scylla on platforms that still have no python3
available (centos7), so we need to keep scylla-gdb.py python2
compatible.

Refs: #7014
Signed-off-by: Botond Dénes <a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>
Reviewed-by: Benny Halevy <23c997c90eb8537635e9392d48e7af1bf1b2ca22@scylladb.com>
Message-Id: <20200811093753.1567689-1-a584fa4d75a0a85d721f44fb6e06315a2853b0b6@scylladb.com>

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