[bitcoin/bitcoin] Docker is not suitable for gitian building (#14061)

Tested on 0.17.0rc1 Linux.

Building on the `bionic` host using LXC:
«`
Generating report
43a6407423d2238d07cf6ec1e254abee30744c8704eb3637d17421eb434eddcf bitcoin-0.17.0-aarch64-linux-gnu-debug.tar.gz
1bd6b9389bd6c068a7e81a6b4d2690d4ff07843602d44198b777c1c1d86feeee bitcoin-0.17.0-aarch64-linux-gnu.tar.gz
eafddf86304f5539146cccd6827f3c468d7d485a5436b17fce72c6086d533e43 bitcoin-0.17.0-arm-linux-gnueabihf-debug.tar.gz
71891132e9f12ebc84380e1f6c3cac81658fb11b01c863481b010ae62dcb8b8f bitcoin-0.17.0-arm-linux-gnueabihf.tar.gz
b53eb323c8fd2b4172459c6d7310817c6f77eaadaaec1568008205fd6c90fdc7 bitcoin-0.17.0-i686-pc-linux-gnu-debug.tar.gz
d329bcdf7a816f83cc70c5fcde561ed9da4ad32f9bc2b7a2fc6093e3e2e307ff bitcoin-0.17.0-i686-pc-linux-gnu.tar.gz
fcf48d67c78a8db7c863b1c1e09d97905244e63fd5c88f6937bd2175b6569003 bitcoin-0.17.0-x86_64-linux-gnu-debug.tar.gz
51eb52972beee5cc41a76920d22a0945460b06e09e7223aa7250cd8d77f7c156 bitcoin-0.17.0-x86_64-linux-gnu.tar.gz
9ddaaf6f24bf41a449dcf7653bc47ff834c6748f11031371f9ab8e3997cd960e src/bitcoin-0.17.0.tar.gz
«`

Building using Docker `bionic` container (on Debian 9):
«`
Generating report
2c04dffc753103c945782ee7c523629507b5c585b127a1201ced04e2663db6b1 bitcoin-0.17.0-aarch64-linux-gnu-debug.tar.gz
206bd76c81e2b8e87388748140340e11a1e87e6b791db791397d5480c57bbee9 bitcoin-0.17.0-aarch64-linux-gnu.tar.gz
6d0898a9f358b6b2e586e6e712c933de6c0f7badfb6a8a162f949bf21149b375 bitcoin-0.17.0-arm-linux-gnueabihf-debug.tar.gz
aa26754f65f65933276924b6e7cf495443550cf0533ecfa2d9ac598ae4acefbf bitcoin-0.17.0-arm-linux-gnueabihf.tar.gz
8f972b1b381c0374b5b2be5d9e04d940b7f8c7c6495ea524fd3221993937306a bitcoin-0.17.0-i686-pc-linux-gnu-debug.tar.gz
e9f3b1dd39e87d45988d352493a8502d6f02a9cc4b5ae8ac622093b36914c50c bitcoin-0.17.0-i686-pc-linux-gnu.tar.gz
db7582930918d2bec7fe293255f9683489d4ca344e3f18329971692982e38015 bitcoin-0.17.0-x86_64-linux-gnu-debug.tar.gz
c7c606dfa5803d51e6a7fbc193dd8e36b32c4f40f4944e5984fd809028cc0cbf bitcoin-0.17.0-x86_64-linux-gnu.tar.gz
9ddaaf6f24bf41a449dcf7653bc47ff834c6748f11031371f9ab8e3997cd960e src/bitcoin-0.17.0.tar.gz
«`

Only source tarballs are the same.
It seems Docker `bionic` container is not suitable for reproducible building.