lisk_snapshot.sh: dump directly from database

[fchavant]

Expected behavior

• stop application
• copy database
• run on copy:
  • TRUNCATE peers;
  • TRUNCATE mem_accounts2u_delegates;
  • TRUNCATE mem_accounts2u_multisignatures;
• pg_dump the copy and gzip it

Actual behavior

We run the application the application with the -s switch and wait for it to exit before creating a dump file.

Steps to reproduce

Run lisk_snapshot.sh

Which version(s) does this affect? (Environment, OS, etc...)

1.6

[MaciejBaj]

The direct cause of #3119.