Dspash fixes

[tammam1998]

Fixes many bugs and reliability problems:

• Support multiple inputs in hdfs cat "hdfs dfs -cat $IN1 $IN2 .."
• Fix bugs with multi sink scripts
• Support HDFS blocks that are not stored in subdir0 locally
• Merge graph on one worker on the first aggregator (Performance improvement)
• Use processes instead of threads in workers (fixed hanging issue)
• Fixes other bugs and edge cases in graph splitting
• Setup and Installation scripts improvements

[github-actions]

OS:ubuntu-20.04
Tue Jun 7 17:59:51 UTC 2022
intro: 2/2 tests passed.
interface: 34/34 tests passed.
compiler: 54/54 tests passed.
agg: 109/109 tests passed.

[github-actions]

OS:ubuntu-18.04
Tue Jun 7 18:00:15 UTC 2022
intro: 2/2 tests passed.
interface: 34/34 tests passed.
compiler: 54/54 tests passed.
agg: 109/109 tests passed.

[github-actions]

OS = Debian 10
CPU = Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz
Ram = 15752
Hash = 226346a
Kernel= Linux 4.15.0-167-generic x86_64

benchmark	tests	passed	failed	untested	unresolved	unsupported	not_in_use	other_status
posix	494	375	41	31	6	40	1	0
intro	2	2	0	0	0	0	0	0
interface	34	34	0	0	0	0	0	0
compiler	54	54	0	0	0	0	0	0
aggregator	109	109	0	0	0	0	0	0

[angelhof]

I would prefer redirecting these changes to a different branch (other than future). Let's have a dspash-future branch that we will work on temporarily, and when everything stabilizes, we can push to the normal future (to avoid stalling on PRs now). We can still make PRs to this dspash-future branch.