Make releasedata.Product usable in 'with' expression (#294)

This way the writing of the JSON file is handled automatically if the update does not fail.
It pave the way to further global improvements, such as a better error handling.

src/gke.py

@@ -13,18 +13,16 @@ URL_BY_PRODUCT = {
 }
 
 for product_name, url in URL_BY_PRODUCT.items():
-    product = releasedata.Product(product_name)
-    relnotes = http.fetch_url(url)
-    relnotes_soup = BeautifulSoup(relnotes.text, features="html5lib")
+    with releasedata.ProductData(product_name) as product_data:
+        relnotes = http.fetch_url(url)
+        relnotes_soup = BeautifulSoup(relnotes.text, features="html5lib")
 
-    for section in relnotes_soup.find_all('section', class_='releases'):
-        for h2 in section.find_all('h2'):  # h2 contains the date
-            date = dates.parse_date(h2.get('data-text'))
+        for section in relnotes_soup.find_all('section', class_='releases'):
+            for h2 in section.find_all('h2'):  # h2 contains the date
+                date = dates.parse_date(h2.get('data-text'))
 
-            next_div = h2.find_next('div')  # The div next to the h2 contains the notes about changes made on that date
-            for li in next_div.find_all('li'):
-                if "versions are now available" in li.text:
-                    for version in VERSION_PATTERN.findall(li.find('ul').text):
-                        product.declare_version(version, date)
-
-    product.write()
+                next_div = h2.find_next('div')  # The div next to the h2 contains the notes about changes made on that date
+                for li in next_div.find_all('li'):
+                    if "versions are now available" in li.text:
+                        for version in VERSION_PATTERN.findall(li.find('ul').text):
+                            product_data.declare_version(version, date)