Add shellcheck to the CI

Updates our scripts to pass. Achieves POSIX compliance for
`increase_default_stack_size.sh` via replacing `hexdump` with `od` and `tr`.
Replaces the non-POSIX `dd status=none` with the POSIX `dd 2> /dev/null`.

orchestration/testnet/networks/bitcoin/run.sh

@@ -1,9 +1,10 @@
 #!/bin/sh
+set -e
 
 RPC_USER="${RPC_USER:=serai}"
 RPC_PASS="${RPC_PASS:=seraidex}"
 
 bitcoind -testnet -port=8333 \
-  -rpcuser=$RPC_USER -rpcpassword=$RPC_PASS \
+  -rpcuser="$RPC_USER" -rpcpassword="$RPC_PASS" \
   -rpcbind=0.0.0.0 -rpcallowip=0.0.0.0/0 -rpcport=8332 \
   --datadir=/volume