genfio: Splitting gen_template in 2 parts

gen_template can be split in to two parts:
- the static headers
- the dynamic ones linked to the arguments from cmdline

The static ones are now in gen_template() call before parsing the
cmdline.

The dynamic ones are now call in finish_template() after parsing the
cmdline.

That also open the ability of feeding the fio header during the parsing
removing the need of specific variables to remember the values.
genfio: Adding exec_{pre|post}run support

It's pretty useful being able to run some commands before or after a
job. That could be use to ask some external storage array to loose its
cache or return in a particular configuration state.

The -A (stands for After) or -B (stands for Before) allow user to define
what commands shall be run before or after a job.
genfio: Don't use cat EOF for small prints

That's just bother the reading when very few data is involved. A simple
print is enough
genfio: Use dynamic default values in help

To avoid mismatch between default values and help, let's print directly
the default value of the option.
tools: Adding gitignore

Nothing like a clean git status ;o)
genfio: Protecting parse_cmdline from spaces

If you want to provide arguments with spaces in it, $@ shall be
protected with quotes.

That's required to manage complex cmdline for -A or -B options
fio2gnuplot: Fixing Yaxis rendering for 2D plots

With many values, gnuplot was complaining about too many ticks like :

"graph2D.gpm", line 26: warning: Too many axis ticks requested (>9e+03)

Using the "auto" command, that works much more better and axis are now
readable