models: replace workflow.run_number with generation and restart number

[giuseppe-steduto]

Change the workflow table to split the run_number into two integers: one referring to the generation of the workflows, and the other one referring to the restart number, thus removing the limit of 9 restarts.

Closes #186.

---

To test the PR, these quick scripts might be come in handy:

1. Run the specified number of workflows on REANA (default 15), to be run from a workflow directory (such as roofit).

#!/bin/bash

# Set the default number of runs to 15 if no argument is passed
NUM_RUNS=${1:-15}

# Run the setup environment command
eval $(reana-dev client-setup-environment)

# Run the workflow the specified number of times
for (( i=1; i<=NUM_RUNS; i++ ))
do
  echo "Starting run $i of $NUM_RUNS..."
  reana-client run -w root6-roofit
  echo "Run $i submitted."
done

2. Restart a specific generation of the roofit demo workflow (default 1) a certain number of times (default 15). ./restart.sh 50 3 will restart root6-roofit.3 50 times.

#!/bin/bash

# Set the default number of runs to 15 if no argument is passed
NUM_RUNS=${1:-15}
TO_RESTART=${2:-1}

# Run the setup environment command
eval $(reana-dev client-setup-environment)

# Run the workflow the specified number of times
for (( i=1; i<=NUM_RUNS; i++ ))
do
  echo "Starting restart $i of $NUM_RUNS..."
  reana-client restart -w root6-roofit.$TO_RESTART
  echo "Restart $i submitted."
done

[codecov]

Codecov Report

Merging #205 (589978b) into master (1fde517) will increase coverage by 0.20%.
The diff coverage is 93.33%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #205      +/-   ##
==========================================
+ Coverage   74.24%   74.44%   +0.20%     
==========================================
  Files           7        7              
  Lines         893      900       +7     
==========================================
+ Hits          663      670       +7     
  Misses        230      230              

Files	Coverage Δ
reana_db/config.py	0.00% <ø> (ø)
reana_db/models.py	90.30% <95.83%> (+0.05%)	⬆️
reana_db/utils.py	76.29% <83.33%> (+0.08%)	⬆️

[mdonadoni]

Works well!

[mdonadoni]

Amazing job! Everything works well 🚀