revive Linux_i386; upgrade ubuntu 16.04 (not supported starting dec 2021) => 18.04

[timotheecour]

• upgrade ubuntu 16.04 (not supported starting dec 2021) => 18.04
• revive Linux_i386 (refs CI fails on azure 32 bit linux Linux_i386: sudo apt-fast install fails #17325) ; looks like working now (might break again in future but at least we can keep it on while it behaves )

refs:

##[warning]Ubuntu 16.04 LTS environment is deprecated and will be removed on September 20, 2021. Migrate to ubuntu-latest instead. For more details, see https://github.com/actions/virtual-environments/issues/3287.
,##[error]The job running on agent Hosted Agent ran longer than the maximum time of 90 minutes. For more information, see https://go.microsoft.com/fwlink/?linkid=2077134
,##[warning]Agent Hosted Agent did not respond to a cancelation request with 00:05:00.
Agent: Hosted Agent
Started: Today at 2:46 PM
Duration: 1h 34m 59s

Job preparation parameters
7 queue time variables used