CNS-578: small fixes for init chain scripts

[oren-lava]

init_chain.sh - if jq is not installed, the script fails. Added jq installation
init_chain_commands.sh - added another wait_next_block after proposals to avoid statistical account sequence mismatch error

[orenl-lava]

while at it, I noticed the OS-specific logic for sed (twice) in there. it can be simplified by doing:

case "$(uname)" in
  Darwin)
    SED_INLINE="-i ''" ;;
  Linux)
    SED_INLINE="-i" ;;
  *)
    echo "unknown system: $(uname)"
    exit 1 ;;
esac

...
sed $SED_INLINE ...
...

with this only one copy of (each relevant) sed command is needed and is useful for both.
(disclaimer: not tested on Darwin, but the idea should be clear).

fixed